1. Field of the Invention
This invention relates to a method for producing materials, including films and nonwovens, having z-direction folds or ridges on at least one surface of the material. This invention further relates to a lofty, nonwoven material produced from continuous fibers in which the lofty character of the nonwoven material is the result of the fibers comprising the web having a z-direction orientation, whereby a plurality of ridges or folds are formed on at least one surface of the nonwoven web. These materials may be particularly suitable for use in a broad range of applications including fluid management (surge), air and liquid filtration, acoustic and thermal insulation, packing material, absorbents, and cleaning materials. More particularly, these materials may be suitable for use as surge, spacer layers, filtration materials and absorbent layers in personal care absorbent products including disposable diapers, incontinence garments, and feminine care products such as sanitary pads and napkins, and in face masks, surgical gowns, sterile wraps and surgical drapes.
2. Discussion of the Related Art
Absorbent personal care articles such as sanitary pads and napkins, disposable diapers, incontinent-care pads and the like are widely used, and much effort has been made to improve their effectiveness and functionality. These articles generally include a liquid absorbent material backed by a liquid-impervious barrier sheet. To enhance the sense of comfort, the absorbent material has a facing of a material which masks at least the body-facing surface of the product. The purpose of this cover material is to help structurally contain the absorbent material and to protect the wearer from continuous direct contact with moisture from previously wetted absorbent material. The cover material is typically of relatively low basis weight nonwoven fabric. Improved product performance has been obtained in these products through the incorporation of a surge management material disposed between the cover material and the absorbent material. The surge management material is made from a relatively high basis weight, low density, that is, thick, nonwoven web material.
In nonwoven webs, the fibers comprising the web are generally oriented in the x-y plane of the web and the resulting nonwoven web material is relatively thin, that is lacking in loft or significant thickness. Loft or thickness in a nonwoven web suitable for use in personal care absorbent articles promotes comfort (softness) to the user, surge management and fluid distribution to adjacent layers.
In order to impart loft or thickness to a nonwoven web, it is generally desirable that at least a portion of the fibers comprising the web be oriented in the z-direction. Conventionally, such lofty nonwoven webs are produced using staple fibers. See, for example, U.S. Pat. No. 4,837,067 which teaches a nonwoven thermal insulating batt comprising structural staple fibers and bonding staple fibers which are entangled and substantially parallel to the faces of the batt at the face portions and substantially perpendicular to the faces of the batt, and U.S. Pat. No. 4,590,114 which teaches a batt including a major percent of thermo-mechanical wood pulp fibers stabilized by the inclusion of a minor percent of thermoplastic fibers including staple length thermoplastic fibers. Alternatively, conventional high loft forming processes rely on pre-forming processes such as fiber crimp formed on a flat wire or drum, and post-forming processes such as creping or pleating of the formed web.
In contradistinction to the known art, the present invention does not first form a web of material and pleat it. Rather, fibers are looped on themselves without first being formed into a material web. These fiber level loops, running from a first major surface of the web to a second major surface, are aggregated in the cross machine direction to form ridged structures herein sometimes called xe2x80x9cwavesxe2x80x9d or xe2x80x9cfoldsxe2x80x9d to distinguish them from xe2x80x9cpleatsxe2x80x9d which refer to structures in preformed web or mesh material that has been folded on itself. A xe2x80x9cwavelengthxe2x80x9d may generally be considered the transit of a loop between its successive trough points on one major surface of the web.
Accordingly, it is one object of this invention to provide a lofty nonwoven web material comprising substantially continuous fibers as opposed to staple fibers traditionally used in the manufacture of such nonwoven materials.
It is yet another object of this invention to provide a method for producing nonwoven materials having z-direction orientation portions.
These and other objects of this invention are addressed by a method for producing a material having z-direction folds comprising conveying a substantially unformed and flat base material of substantially continuous fibers, and added materials if desired, on a first moving surface into a nip formed by the first moving surface and a second moving surface, the second moving surface traveling at a slower speed than the first moving surface, resulting in formation of a plurality of z-direction folds on at least one surface of the material. The method of this invention conveys a material by means of a moving surface into a confined space (the nip) and removes it from the confined space by means of a second moving surface, whereby the rate of removal of the material from the confined space is slower than the rate of material input to the confined surface, resulting in formation of a nonwoven material having z-direction components. The z-direction components produce ridges or ripples on both the major, or x-y surfaces of the material. According to this method the extent of the ridges, and thus the character of the resulting material formed, may be easily affected by a number of operating parameters including, but not limited to, the type of material being processed, geometry of the confined space, the means for transferring the material in the confined space from the first moving surface to the second moving surface, presence or lack of a binding agent such as an adhesive, and the relative speeds of the first and second moving surfaces.
Typically, the size of the confined space (nip) and the relative speeds of the moving surfaces are related with respect to the formation of a web having a desired density of folds. For example, for very low differential speeds between the two moving surfaces, the size of the nip will be very small. As the differential speeds increase, the size of the nip will also increase.
According to the embodiments herein, a material of this invention, as produced with the method of this invention, comprises a nonwoven web with a plurality of substantially continuous fibers having a z-direction orientation and forming a plurality of folds or ridges on the major surfaces of the nonwoven web.
In one embodiment according to the present invention a lofty nonwoven web, made with fibers looped on themselves, is made in a first configuration. This first configuration of the lofty web is made with regularly shaped ridges extending from the plane of the web in the z-direction, and occurring with regular pattern or periodicity in the machine (x-axis) or cross machine (y-axis) directions with the ridges lightly fixed in the first configuration. The first configuration of the ridges is broken and reset to a second predetermined configuration such as by controlled stretching. The ridges are then fixed in the second configuration, resulting in a new shape and periodicity of the ridges. The second configuration thus has no adhered leading or trailing edges of the ridge waveform. The second configuration is generally one which is unattainable through the process used to make the first configuration. The material is particularly useful for filtration media or other fabric structures where a known ridge shape and periodicity is desired. This embodiment may also be utilized for control of the periodicity and pleat shape of a previously pleated web.
In yet another embodiment, the present invention seeks to create, and utilize the advantages of, a lofty nonwoven web of continuous fibers having z-direction fibers but without discernable ridge structure which would lead to fluid channelization and other inherent characteristics of the ridge structure which may be undesirable for certain applications. Accordingly, among the objects of this embodiment is to provide a lofty nonwoven web material comprising substantially continuous fibers as opposed to staple fibers traditionally used in the manufacture of such nonwoven materials and to provide for producing nonwoven materials having z-direction portions with an undifferentiated mass of loops or pleats to create a web of material with no discernable ridge structure and no defined fluid channels.
In still another embodiment of the present invention, a precursor material having differential basis weight is formed using a three dimensional forming surface, which may be a wire or a formed membrane. Bands of higher and lower basis weight are thus formed, preferably running in the cross direction and alternating in the machine direction for the precursor web. The precursor material is then pleated, or folded, with the folds generally occurring along the borders between the higher and lower basis weight bands. The resultant lofty web material may then have major surfaces in x-y planes of a first basis weight material and interstitial material between the major surfaces in the z-direction composed of a second and different basis weight material. Alternatively, only one major surface may be higher basis weight material or, pleats of alternating high basis weight and low basis weight pleats may be produced in a single sheet. The material is particularly useful for fabric structures where a known ridge shape and periodicity is desired.